LogDog: Implement prefix registration in Butler.

client/internal/logdog/butler/butler_test.go

Index: client/internal/logdog/butler/butler_test.go
diff --git a/client/internal/logdog/butler/butler_test.go b/client/internal/logdog/butler/butler_test.go
index 782b9df6782e0e3445ac6469d34ff8e89acc2905..55aa8531ae4590df4a894c4515d0d1ea2f263a8f 100644
--- a/client/internal/logdog/butler/butler_test.go
+++ b/client/internal/logdog/butler/butler_test.go
@@ -231,7 +231,6 @@ func TestConfig(t *testing.T) {
 			Output:  &to,
 			Prefix:  "unit/test",
 			Project: "test-project",
-			Secret:  types.PrefixSecret(bytes.Repeat([]byte{0x55}, types.PrefixSecretLength)),
 		}
 
 		Convey(`Will validate.`, func() {
@@ -282,7 +281,6 @@ func TestButler(t *testing.T) {
 			BufferLogs:    false,
 			Prefix:        "unit/test",
 			Project:       "test-project",
-			Secret:        types.PrefixSecret(bytes.Repeat([]byte{0x55}, types.PrefixSecretLength)),
 			TeeStdout:     &teeStdout,
 			TeeStderr:     &teeStderr,
 		}